The present invention relates to an independent paper feeder usable with a copier and others for feeding papers and, more particularly, to a paper feeder of the type having trays which are arranged one above another and a paper feed unit which is situated in front of the trays and caused to begin sheet feed after being elevated or lowered to a selected position. Still more particularly, the present invention relates to the control of paper transport speed and the detection of amounts of remaining papers in the trays of such a paper feeder.
A problem with a prior art paper feeder of the type described is that when the paper feed unit is moved up and down at high speed, the resultant increase in inertia prevents the unit from being stopped with accuracy at a selected paper feed position and, thereby, deteriorates the performance of the paper feeder. Typical occurrences are that papers are not fed at all and that two or more papers are fed together. Although the travelling speed of the unit may be lowered in order to enhance the accuracy with which the unit is stopped, such brings about another problem, i.e., long travel time and poor operating efficiency.
It has been customary to furnish each of the trays of the paper feeder with a sensor responsive to an amount of papers remaining in the tray. This is disadvantageous, however, since as many sensors as the trays have to be installed at the sacrifice of cost. In another known system, a remaining amount of papers is detected when the paper feed unit is stopped at a selected one of the trays. A drawback with this system is that the amounts of papers in the respective trays cannot be displayed when a power source is turned on, resulting in poor operating efficiency.